Technics SL1200/1210 debate

Valves are not linear. If you 'push-pull' in Class A then the non-linearities cancel out to some extent. You can then use negative feedback to tidy things further.

A SET usually has no feedback and no mutual cancellation. Hence more distortion.

I think.

Paul

 

It does depend on how hard the SET o/p stage is being asked to work.

Very sensitive speakers (presenting a benign load) used in conjunction with a SET amplifier can allow an well designed output stage to operate with sufficiently low levels of distortion.

However, many SET amplifiers are heard when coupled to inappropriate loudspeakers and can sound very poor.

It can be a good thing to have simple circuitry with few gain stages. It can also be a good thing to use speaker drivers in such a way that they don't have to move very far to generate a given spl.

I suppose it depends on how one feels about the use of nfb, op amps etc. If they are considered to be perfectly transparent with no audible side effects then SET's and suchlike appear foolish & unnecessary. If, on the other hand, a person feels that Op Amps, negative feedback (& active filtering using feedback) along with complicated high power amplifiers & long throw drivers have no place in audio systems and spoil the sound of music played through them, then that person will doubtless disagree. It takes all sorts.

Some people prefer the sound of SET amplifiers and efficient speakers. Others prefer the character & colouration added by a deck like the LP12. Others might say that digital amplifiers incorporating room correction are the only way to go. Telling any of them that they are wrong or that they are not achieving 'hifi' will not alter their perspective one iota. They will say that music reproduced in this way sounds more like and gives more the feeling of music as they hear it at a live event.

Oranges or apples. Which is more fruity?

 

But how does 'that sort' reconcile how the music got onto the record or CD with their distaste for 'nfb, op amps etc'?

SETriodes are popular despite SETransistors offering the advantages (simplicity and amenable distortion...) but reducing the disadvantages (cheaper, cleaner, less power consumption, more power output). The only common SE Transistor I can think of at the moment is the JLH Class A.

(I see more ludicrousness from 'anthonyTD' on the other side. I wonder what the chances of anybody picking him up on it are?)

Paul

 

the same way, I suppose, that people who like 'modern' technology can appreciate the quality of recording that Decca, EMI, Capitol, Contemporary etc managed to achieve with valve gear. (I generally prefer the quality of those older recordings although some of that may sometimes have been down to more care having been taken too) I think EMI & Decca's classical recordings for example had qualitatively deteriorated by the early to mid 70's. As had Blue Note's.

Point me at a modern vocal recording as good as Nat King Cole's on the Capitol LP he did with George Shearing (for example) or some classical as nicely done as some of RCA's 2000 series & I'd perhaps have more appreciation of the wonders of modern tech.


I once built a JLH 10W class A! It was single rail but not quite single ended iirc. 2 devices, o/p coupling cap & some kind of phase splitter driver arrangement (ztx651?) It did sound quite good though not as good as a simple UL pair of EL84's might.

I'm sure TdeP made a proper, ludicrously inefficient, SE transistor amp at one point (Yoshino?)
I saw them (mono's iirc) but didn't get to hear them. Indeed, he appears to be making something similar again with output transformers although I don't know if it's SE.

 

My 2p, FWIW, IMO, YMMV, etc:

Valves (especially triodes) are certainly more linear than bi-polar transistors. That's the point of using them - they're just about linear enough to use without the crutch of feedback. I'm of the opinion that the better the open-loop linearity, and the less compensation (feedback) you need to use, the better. I believe this brings benefits when used appropriately, i.e. with high-sensitivity speakers and a benign impedance curve to minimise the problems (which are real). Of course they're going to perform poorly when partnered inappropriately. Not all speakers require the lowest damping factor possible - for some (e.g. old Tannoys, having a slightly higher Zout can help in the bass).

In this context SE vs PP in not relevant - the output impedance is likely to be similarly high for both topologies in the absence of feedback. The distortion cancellation in PP will only work on even-order products leaving the odd-order distortion (and possibly even increasing it). There is empirical evidence to show that odd-order is more subjectively objectionable, so perhaps not as beneficial as it initially seems. Feedback tends to decrease low-order distortion but will add higher order products at low level. Is this audible? Maybe, maybe not. Judging by the feedback vs non-feedback amps I've heard (SE AND PP) I believe it is.

It is possible to get some distortion cancellation in SE, between driver and output tubes - people have experiments with reversing the polarity of the signal from the driver to the output and measured a marked decrease in distortion connected one way over the other. This is however *extremely* unpredictable and I don't believe anyone who claims to be able to predict it. It's more luck than judgement.

I'm also of the opinion that JFETs can be rather good they're more linear than bi-polars - Nelson Pass has done a lot of work with these recently in his First Watt experiments, successfully using them without feedback. The F1 & F2 are interesting in that they are basically the same except one is SE, one is PP, both have pretty low distortion. The F1 being SE has a mainly even order distortion spectrum, while the F2 is PP and has a mainly odd-order spectrum. They have different flavours in the same way that PP and SE amps are reported to have.

I heard an F3 - which I thought a very fine amplifier (it user Lovoltech power JFETs). Switching to a 'high distortion' SE tube amp brought about a significant subjective increase in clarity. Go figure. I would love to know why, myself.

In summary, SETs can give excellent results due to the good open-loop linearity and simplicity (which I see as a virtue). I'm not blind to the faults, high Zout, highish distortion, but sometimes the cure is worse than the disease. I'll use whatever gives me the best subjective results with music.

I'm not going to get into the other part.

 

It's an unanswerable question. One possibility is that since the late 1950s professional recording equipment has been adequate and development means cheaper, more channels, more processing possibility, more editing facilities. You could make a 50s recording with 00s equipment, but nobody has the resources, and it would sound like a 50s recording so nobody would want to buy it. Especially since it wouldn't feature Nat King Cole...

I think it qualifies because it uses an active load in place of a transformer (or the alternative straight resistor). It's not 'push pull' in the usual sense of a symmetrical output stage. The original WW articles still make entertaining reading.

 

For the watchers still confused about 'linearity' go to http://www.westernelectric.com/spec_sheets/300B.pdf print page 3 and put a ruler against the curves in the lower graph.

Paul

 

Wow! Way to mis-present information. Perhaps drawing a load line might be more useful.



The important thing is the line spacing but then you knew that.

The typical bi-polar don't look so good in comparison.



Please explain how something that follows an exponential law (bipolar) can be more linear than something that follows a 3/2 power (triode) law? Even a JFET is less linear but is closer because it follows a quadratic law.

 

That's the upper graph... I was looking at the transconductance graph.

You're back to ascribing degrees to 'linearity' without consideration of the other factors. I'm not sure what the point of your FET curves is.

IMO the distinction is that a transistor has (relatively) huge transconductance. It 'degenerates' into rather good linearity. Unless you are completely phobic about local feedback. Which might make an interesting discussion.

As would the contrast between the olde-worlde valve amp designers and manufacturers, Williamson, Walker, Leak, Radford, Hafler etc. where the aim was to make an amp that was 'good' in conventional ways using the available technology, and the contemporary movement for valve amps that are 'bad' in a conventional sense.

Paul

 

The "lower graph on Page 3" is the graph of plate characteristics. I guess you meant the top graph on page 5? I posted the FET curves for comparison, because that's what I assumed you were talking about from your statement.

Absolutely right, I'm talking about intrinsic device characteristics, in the absence of other factors, i.e. as starting point. If you build a straight transconductance amplifier with a tube and a transistor, the tube version will be more linear (accepting that a bipolar isn't a transconductance device anyway). How much does the Gm curve of a FET very without any sort of compensation? I'd wager more than the 300B. Your position seems to be that you can add local degenerative feedback to linearize it? Sure you can, but you're no longer comparing just the devices. And you can use local degeneration with tubes as well.

Anyway, I've had good results with local feedback in tube driver and voltage gain stages, so no, no phobia. There's some argument over whether a triode has an internal feedback mechanism, because a triode can be modelled as a pentode with feedback.

As I've said before, I don't think global feedback is the panacea it's made out to be and a better starting position works in your favour. Tubes tend to promote simplicity and simplicity is nearly always a virtue. It appeals to the engineer in me.

Anyway, Nelson Pass seems to agree and he makes some nice sounding stuff. He seems to be using some cute new devices, have a read here:

http://www.firstwatt.com/downloads/J2 Power Amplifier pdf.pdf

Sadly, they Semi-South SiC JFETs are exorbitantly priced for now.

 

The page which in the PDF has 'Page 3 - 300B' at the top.

No matter.

But you're comparing curviness without considering how much of the curve you're looking at. Obviously as you pick points on any curve that are closer together the section of curve between them tends towards linear. I don't think you can discard the operating range when making a comparison.

Fundamentally I think it is. Collector current is related to Vbe in a consistent way. The consequent base current varies according to temperature, mood and time of the month.

I would be surprised if many people, in principle at least, disagreed with the latter. And global feedback is definitely not a 'panacea'.

I like Nelson Pass.

I think it's largely a matter of preferred style. But when it comes to SETs operating at or beyond audible distortion, especially very expensive commercial varieties, it's legitimate to ask 'why?'.

Paul

 

Sure, I don't disagree. Taking the 300B example, it will progressively become less and less linear as you increase level, but in a nice predictable way.

Yes, fair enough. I was thinking of the simple current model. But the Ebers-Moll equations shows that Gm varies with current and is therefore non-linear in the same way as for a tube. The temperature term is also of particular interest because of the low thermal mass compared to a tube.

Heh, well, reading what some people post, you'd believe it was some kind of magic bullet. Perhaps I'm simply over-reacting to that.

I'd agree, operating them inappropriately is stupid, they're not magic, and there is a lot of bullshit around SETs. I get tired of it too, and I like them. In fact they are very specialised and need to be used within a specific approach to work well. Driving a conventional lowish sensitivity loudspeaker, I wouldn't expect good results. While some people think distortion doesn't matter, I think that's cobblers, yes, it does. But, used carefully they can give good results.

But what about say 300B class-A PP with no feedback? They also suffer from the same problems as SETs WRT Zout and distortion, the even-order cancellation only helps a bit. Though I will happily admit that SE transformers are an order of magnitude more difficult.

 

Back on topic..it could be some sort of advertised "Webinar" with posting limited to x number of posters and by invitation only.

Might be just what Zerogain needs to stimulate readership and encourage participation.

 

Rob, I don't actually have a deck. My recent streaming/downloads onto a very capable DAC experiences in the Wirral area yesteday may yet obviate the need....

 

That is now a fine solution and works very well.

I was with a friend streaming into a very capable dac in the Rochdale area yesterday and today

 

The DAC will be with me within a couple of weeks. It is being built to order and won't actually have a valve output stage after all. Duncan (Tubehunter) believes that it is not necessary to have two valve stages including the pre that follows.

With the DAC in place (being fed by my CD transport to begin with) I then go cap-in-hand for advice on all the other bits -hardware and software to make streaming/downloads in FLAC and hi-res work for me. I'm a completely blank piece of paper on this.

 

Indeed, pfm offers no protectionism whatsoever for it's trade members. This is exactly as it should be. The only things I won't host are libel or 'customer service desk' threads (i.e. disagreements between a customer and a company relating to a specific purchase). This thread in relation to both Tube Distinctions and Sound Hi-Fi constitutes neither. FWIW I do believe this thread needs a moderation nip & tuck here and there (on both sides of the debate), but it is not really my place to do it.

Tony.

 

Tony, I agree. I've pruned the thread to remove AUP breaches. Sorry guys, but sometimes work gets in the way of mod duties. Let's please get back on topic.

 

Further experiments show that I initially misjudged the Jelco SA-750D. It is not thin. It actually has a well-nourished low and mid bass range. I fell for the effects of a cartridge which, despite being well run in, had not been used for a while and needed to wake up again. Mea culpa for judging prematurely.

More expensive arms will sound clearer, rach higher and lower and resolve instrumental timbre better, but the Jelco is truly superb value for money. Its greatest strength is a good sense of PRaT. A good flat earth arm, even with the removable headshell.

 

David Price

If you are David Price the reviewer then please stay away from anything technical as it's obvious you have picked things up from only talking to technical folk. A little knowledge etc etc.

You can build a transistor circuit to be a voltage controlled current amplifier. You can also build a transistor circuit to be linear from 0Hz to 200Khz (well outside the audio band).
very little negative feedback and normal levels of feedback makes no difference...it's still feedback.

That whole last paragraph about transistor circuits was obvious written by someone that has no idea about electronics.